The present invention relates to a device, system, and method of using a turbine flow meter to measure recovered vapor in a vapor recovery-equipped fuel dispenser.
Many fuel dispensers in a service station environment are now equipped with vapor recovery in order to meet governmental regulations. As fuel is being dispensed into a vehicle fuel tank, vapors that are present in the vehicle fuel tank exit out of the vehicle""s fuel tank fill neck. Vapor recovery-equipped fuel dispensers are designed to recover all or substantially all of the vapor that would otherwise escape into the atmosphere at the fuel tank fill neck. The nozzle and hose on the fuel dispenser are specially equipped with a vapor return path wherein vapors that exit the fuel tank fill neck during refueling enter into the nozzle and hose and are returned back to the underground storage tank. If the nozzle is not sealed with the vehicle fuel tank fill neck during refueling, an assisted system may be used wherein a vacuum is created in the vapor return line to draw vapors into the vapor return line. An example of such an assist vapor recovery system is described in U.S. Pat. No. 5,040,577, entitled xe2x80x9cVapor recovery system for fuel dispenser,xe2x80x9d now Reissue Pat. No. RE35,238. An example of a non-assisted vapor recovery system wherein a seal is created between the vapor return path in the nozzle and the vehicle fuel tank filler neck is illustrated in U.S. Pat. No. 5,636,667 entitled xe2x80x9cConversion of fuel dispensers to provide for vacuum assisted vapor recovery.xe2x80x9d This system is commonly referred to as a xe2x80x9cbalance system.xe2x80x9d
There are several reasons why a vapor flow meter may be desired in a vapor recovery-equipped fuel dispenser. When vapor recovery-equipped fuel dispensers were first introduced into the marketplace, there was no method of determining whether vapor was actually being recovered. For example, in an assisted system, the vapor pump that creates a vacuum in the vapor return line may be inoperable or not operating properly. In an unassisted system, such as the balance system, the vapor return line may contain a leak such that recovered vapors escape through the leak before reaching the underground storage tank. Fuel dispenser manufacturers have contemplated placing a vapor flow meter in the vapor return line of fuel dispensers in order to measure recovered vapor as one method of verifying that vapors are actually being recovered and returned to the underground storage tank. If the vapor flow meter registers a vapor flow, then vapors are being recovered. The fuel dispenser can analyze the amount of vapor recovered, as measured by the vapor flow meter, to determine if the anticipated amount of vapor is being recovered in relation to the flow rate of fuel being dispensed since vapors are pushed out of the vehicle fuel tank filler neck at a rate proportional to the fuel flow rate being placed inside the vehicle fuel tank.
One example of a vapor flow meter incorporated into an assisted vapor recovery-equipped fuel dispenser is described in U.S. Pat. No. 6,347,649, entitled xe2x80x9cPressure sensor for a vapor recovery system.xe2x80x9d In this system, the recovered vapor enters into the vapor return line and enters into a vapor flow meter inline to the vapor return line. The vapor measurements measured by the vapor flow meter are communicated to a control system. The control system verifies that vapors are being recovered when expected using the measurements received from the vapor flow meter. Also, if it is desired to calculate the vapor-to-liquid (V/L) ratio of the fuel dispenser, which is used to determine the fuel dispenser""s vapor recovery efficiency, a vapor flow meter is needed to measure the amount of vapor being recovered for the xe2x80x9cVxe2x80x9d value in the xe2x80x9cV/Lxe2x80x9d ratio calculation.
Any number of different types of meters may be used to provide the vapor flow meter. Some meters are inferential meters, meaning that the actual displacement of the liquid or gaseous material is not measured. An inferential meter uses some other characteristic other than actual displacement to measure flow rate or volume of recovered vapor. Inferential meters sometimes have advantages over positive displacement meters, including smaller size. One example of an inferential meter that may be used as a vapor flow meter is known as a turbine flow meter, like that described in U.S. Pat. No. 5,689,071, entitled xe2x80x9cWide range, high accuracy flow meter.xe2x80x9d The turbine flow meter described in this patent measures the flow rate of a fluid or gaseous material by determining the number of rotations of a turbine rotor located inside the flow path of the meter.
As vapor enters the inlet port of the turbine flow meter in the aforementioned ""071 patent, the vapor passes across two turbine rotors inside the meter""s housing. The vapor causes the turbine rotors to rotate. The rotational velocity of the turbine rotors is sensed by pick-off coils. The pick-off coils are excited by an a-c signal that produces a magnetic field. As the turbine rotor rotates, the vanes on the turbine rotors pass through the magnetic field generated by the pick-off coils thereby superimposing a pulse on the carrier waveform of the pick-off coils. The superimposed pulses occur at a repetition rate (pulses per second) proportional to the rotors velocity and hence proportional to the measured rate of vapor flow.
However, a problem occurs when using a turbine vapor flow meter such as the one described in the aforementioned ""071 patent. When the fuel dispenser nozzle is disengaged and fuel is no longer flowing into the vehicle fuel tank, vapor is no longer being pushed out of the vehicle fuel tank and into the vapor return line. However, the previous rotational momentum of the turbine rotors inside the turbine flow meter causes the turbine rotors to continue to rotate even after vapor is no longer flowing into the vapor return line. This causes the turbine vapor flow meter to continue generating measurement signals as if vapor was still flowing since the turbine rotors continue to rotate for a certain amount of time after vapor flow stops. The control system that receives the measurement signals from the pick-off coils of the turbine flow meter continues to register vapor flow falsely.
A solution to the aforementioned problem must be found in order to use a turbine flow meter as an accurate vapor flow meter in a vapor recovery-equipped fuel dispenser. The present invention provides a solution to this problem.
The present invention relates to a turbine flow meter used as a vapor flow meter in a vapor recovery-equipped fuel dispenser. The vapor flow meter measures that amount of vapor recovered by the fuel dispenser and thereafter returned to the underground storage tank during a fueling operation. It may be desireable to measure the amount of vapor returned to the underground storage tank as an indication that the vapor recovery system in the fuel dispenser is properly operating, a leak is not present in the vapor return path, and/or calculation of the vapor-to-liquid (V/L) ratio of the fuel dispenser for performance monitoring and/or measurement.
The turbine flow meter is used as the vapor flow meter. The turbine flow meter is an inferential meter that is small in size and highly accurate. The turbine flow meter contains one or more turbine rotors on a shaft inside the turbine flow meter. As vapor passes through the turbine flow meter, the vapor causes the turbine rotor(s) to rotate. The turbine rotor(s) contains a plurality of vanes made out of a magnetic material. A pick-off coil is placed on the meter in close proximity to the turbine rotor(s). The pick-off coil generates an a-c carrier signal that generates a magnetic field around the vanes of the turbine rotor(s). As the turbine rotor(s) rotates, the vanes superimpose a pulse signal on the pick-off coil carrier signal that is detected by the pick-off coil. The pick-off coil communicates the carrier signal with pulses superimposed to a control system inside the fuel dispenser. The pulses are counted to determine the rotational speed of the turbine rotor(s) and thereby to determine the vapor flow rate.
Because the turbine rotor(s) may continue to rotate due to their rotational momentum for some period of time after vapor discontinues flowing through the turbine flow meter, the pulse-encoded carrier signal from the pick-off coil continues to indicate pulses even after vapor recovery has stopped thereby yielding an inaccurate measurement. The present invention involves determining when fuel flow is inactive and has stopped as an indication of when to ignore the pulses on the carrier signal from the pick-off coil. When fuel is no longer flowing, vapor is not being recovered and returned through the vapor flow meter since vapor is only pushed out of the vehicle fuel tank when fuel is being delivered to the vehicle fuel tank.
There are several different techniques to determine when fuel is no longer flowing in a fuel dispenser. In one embodiment, the control system that determines when to ignore the pulses on the vapor flow meter carrier signal uses the pulse stream from the fuel flow meter as an indication that fuel is either flowing or is not flowing.
In another embodiment, the control system that determines when to ignore the pulses on the vapor flow meter carrier signal uses a signal from a flow switch located on the outlet side of the fuel flow meter as an indication that fuel is either flowing or is not flowing. The flow switch generates a signal that indicates whether fuel is flowing or not flowing.
In another embodiment, the control system that determines when to ignore the pulses on the vapor flow meter carrier signal uses a signal that controls the fuel flow control valve located in the fuel flow path. The fuel flow control valve is opened when fuel is allowed to flow, and is closed when fuel is not allowed to flow. The fuel flow control valve signal status indicates whether fuel is flowing or not flowing.
In another embodiment, the control system that determines when to ignore the pulses on the vapor flow meter carrier signal uses a signal that controls the vapor pump for vapor recovery. The vapor pump is activated when vapor is to be recovered, and is deactivated when vapor recovery is no longer required. The vapor pump is activated when fuel flow is allowed and/or begins. Therefore, the vapor pump signal status indicates whether fuel is flowing or not flowing.
In another embodiment, the control system that determines when to ignore the pulses on the vapor flow meter carrier signal uses a signal that controls the vapor valve inline to the vapor return line. The vapor valve is open when vapor is to be recovered, and is closed when vapor recovery is not required. The vapor valve is opened when fuel flow is allowed and/or begins. Therefore, the vapor valve signal status indicates whether fuel is flowing or not flowing.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.